1. Field of the Invention
The present invention relates to a method and apparatus for increasing the temperature of compressed air supplied to an air drying device in which moisture is evaporated or in which dust and moisture is blown off articles traveling past the device without the requirement for an external heating source.
2. Description of the Prior Art
Air drying or blow off devices, such as air knives or air distribution manifolds having a plurality of nozzles, are utilized extensively in industry for directing air under pressure at passing articles to evaporate or blow off water, dust, and debris from those articles. Conventional air knives and air distribution manifolds are often formed as elongated structures that extend alongside or transverse to a conveyor belt or conveyor chain carrying articles to be dried or blown clean.
Air knives are extensively used for drying a wide variety of articles of manufacture, such as plastic soft drink bottles prior to labeling, printed electronic circuit boards, food packaging, and many other products. Conventional pressurized air drying devices in the form of air knives and air nozzles have been used in a wide variety of industrial and commercial processes to remove or control the amount of liquids remaining on the surfaces of products after washing, rinsing, cooling, coating, or to which lubricating fluids have been applied. These same air drying devices have also been used to blow dust and debris from products, as well as to accelerate the heating or cooling of products. Applications for air knife and air nozzle blow off include the processing of printed circuit boards assemblies, machine parts, fabricated metals, plastic trays and totes, conveyor belts, electroplating, assorted textiles, food production and packaging, car and truck washing, and many other applications as well.
It is advantageous to utilize air heated above ambient temperature to increase the effectiveness of air blow off drying devices, such as air knives and air nozzles. While the compression of air within a single stage blower does raise the temperature somewhat above the temperature of ambient air drawn into the compressor, external heating systems are often utilized to create greater temperature increases than can be supplied by a single stage of compression.
Very typically the compressed air traveling to the air drying device is directed past separate in-line heaters, such as those powered by electricity, natural gas, or forced steam. Such heaters raise the temperature of the compressed air before it emanates from the air knife or air nozzle manifold. The heated, compressed air reduces drying time and reduces heating time associated with a wide variety of manufacturing processes. In some systems, on the other hand, the devices to be treated are preheated before reaching the air knife or air nozzle manifold. While conventional external heating systems of this type are effective in assisting the air blow off drying devices in ridding the articles to be treated of moisture and dust, the capital expense, energy consumed, space requirements, and the maintenance costs involved with such secondary heat sources add considerably to the overall cost of manufacture or treatment of the articles being processed.
One prior system has been devised which recirculates air emanating from an air knife back to a turbine air blower. This system is described in U.S. Pat. No. 6,260,231. In this conventional system air is returned from a recirculation trough that has side plates for condensing moisture from the air. The moisture flows to the bottom of the recirculation trough and drains from the drying modules. Moisture is removed from the air by a filter before the air is returned to the turbine air blower. However, the air recirculated in this system is subjected to the cooling effects of moisture on the printed circuit boards, or other objects to be dried before it is recirculated. Also, the air that is recirculated is not at an elevated pressure.